1. Field of the Invention
The present invention relates to wireless modems, particularly to wireless modems realized at least in part by a PCMCIA card, otherwise known as a PC Card(trademark).
2. State of the Art
Integrated circuit cards, particularly cards conforming to the PCMCIA or PC Card(trademark) standard, have become a mainstay of mobile computing. Devices of various descriptions are available in the PCMCIA format, including memory cards, modems, disk drives, etc. The development of mobile computing has resulting in an increased demand in particular for wireless modems.
PCMCIA cards come in different varieties including, in order of increasing thickness, Type I, Type II and Type III cards. Ideally, a wireless modem would be realized in the form of a PCMCIA card such as a Type II card and would fit entirely within a Type II package enclosure. To date, this goal has not been fully realized. Because of the significant transmit power requirements of a wireless modem, existing PCMCIA-based wireless modems are provided with a rather bulky battery enclosed within an extension to the standard Type II card. During stand-by operation, the battery is trickle charged in preparation for future transmission and its attendant high power requirements. During transmission, the extra power required by the wireless modem is drawn from the battery.
A different approach to realizing a wireless modem has been to leverage the investment in existing equipment by interfacing a separate radio transceiver to an existing PCMCIA baseband modem. In this approach, the radio is not PCMCIA-based, and is protocol-specific. That is, the radio implements a particular radio protocol such as AMPS, for example. The radio transceiver therefore cannot be used with other different radio protocols, such as CDPD, PCS, etc., since for each different standard, the radio transceiver is different.
Although the pace of innovation in telecommunications may well defy the notion of a common RF standard, the lack of a common standard results in higher costs to consumers. As demonstrated in the wired computer modem market, market penetration depends heavily on prices reaching a threshold level of affordability. Continued improvements are therefore needed in order to make radio data communications equipment widely affordable.
What is needed, then, is an improved PCMCIA-based wireless modem that achieves the competing dual objectives of versatility and low cost.
The present invention, generally speaking, provides for an inexpensive, PCMCIA-based radio transceiver that interfaces to a separate baseband modem, which may itself be PCMCIA-based or may be an internal modem of a notebook computer. Together, the PCMCIA-based radio transceiver and the baseband modem realize a wireless modem. In order to minimize cost and increase versatility of the resulting wireless modem, the radio transceiver is a relatively unintelligent, protocol-agnostic, slave device that is controlled by commands issued by the baseband modem. The baseband modem may be a hardware modem or a software modem. In either case, the character of the baseband modem may be changed by downloading new software. The radio transceiver may also be exchanged for another within a family of radio transceivers, each of which customized for a particular radio standard. The result is an extremely flexible, extremely low-cost wireless modem solution.